Today, examples of devices using the ink-jet technology include ink-jet printers that jet ink on a medium like recording paper to perform drawing (as used herein “drawing” includes “printing”), and industrial devices that form circuits on substrates. The ink-jet devices include an ink tank for reserving ink, an ink-jet head for adjusting and jetting ink, and a carriage for moving the ink-jet head.
In common conventional ink-jet devices, the ink tank is located above the ink-jet head in the carriage. In these devices, ink is supplied due to the head difference between the ink tank and the ink-jet head.
In devices such as large ink-jet printers or large production devices using the ink-jet technology, the amount of consumed ink is inevitably increased, and accordingly large-capacity ink tanks are used. In this case, the head difference between the ink tank and the ink-jet head varies widely according to how much ink is left, and it sometimes causes troubles.
For example, if the amount of remaining ink is large, the head difference between the ink tank and the ink-jet head becomes large, and accordingly applied pressure on the ink-jet head becomes large. As a consequence, it becomes impossible to maintain enough negative pressure not to leak ink in the ink-jet head, with the result that ink may leak out of the ink-jet head. On the contrary, if the amount of remaining ink is small, the head difference between the ink tank and the ink-jet head becomes small, and accordingly negative pressure in the ink-jet head becomes large. As a consequence, the ink-jet head sucks air, with the result that ink cannot be jetted.
In order to solve these problems, there has been known an ink-jet device in which, instead of providing an ink tank in a carriage, the ink tank is provided in a housing of the main body and below the ink-jet head so that the head difference is eliminated. In this kind of ink-jet device, ink is supplied through a flexible conduit connecting the ink tank in the housing of the main body to the ink-jet head in the carriage.
Further, there has also been known an ink-jet device in which the ink tank is divided into a large-capacity main tank and a small-capacity sub tank, and the main tank is disposed in a housing of the main body and the sub tank is disposed in a carriage. In this kind of ink-jet device, the main tank is connected with the sub tank by a flexible conduit. Normally, ink is supplied from the sub tank to an ink-jet head, and, when the amount of remaining ink in the sub tank becomes small, the sub tank is refilled with ink from the main tank. Here, in order to refill the sub tank with ink from the main tank, pressurizing means in the main tank, or negative pressure generating means in the sub tank is used. With the above structure, because the sub tank in the carriage has a small capacity and the head difference between the sub tank and the ink-jet head is small, the problem of ink leakage or jet failure can be solved.
Japanese Laid-Open Patent Publication No. 266734/2003 (Tokukai 2003-266734; published on Sep. 24, 2003) describes such ink-jet recording device having a main tank in a housing of the main body, and a sub tank in a carriage. This ink-jet recording device includes negative pressure and back pressure generating means in the sub tank, and thereby generates suitable negative pressure and back pressure in the sub tank. In this way, the problem of ink leakage or jet failure is solved.
However, the above conventional structure in which the ink tank is located in the housing of the main body, and in which ink is supplied through a flexible conduit to the ink-jet head provided in the carriage poses the following problems.
In the ink-jet recording device having the above structure, in order to supply ink from the ink tank in the housing of the main body to the ink-jet head in the carriage, the flexible conduit needs to be filled with ink. In this case, because the flexible conduit leads from the ink tank in the housing of the main body to the ink-jet head in the carriage, the amount of ink needed to fill the flexible conduit is inevitably increased compared with an ink-jet device in which the ink tank is provided in a carriage. Further, in larger devices, because the length of flexible conduits increases, this problem becomes more serious. As the above example shows, in the conventional ink-jet recording device that has the ink tank outside the carriage and supplies ink through the flexible conduit, a problem occurs that more ink is consumed compared to an ink-jet device in which the ink tank is provided in a carriage.
Further, in the ink-jet device with two ink tanks (main tank and sub tank) as reported in the above Japanese Laid-Open Patent Publication No. 266734/2003, the problem of increased ink consumption also occurs because the flexible conduit connecting the main tank and the sub tank needs to be filled with ink.